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Please check http://www.friedhoff.org/posixfilecaps.html to get more
information on POSIX File Capabilities.
Example: how to remove the SUID root bit from /bin/ping?
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Make sure you have kernel 2.6.24 or newer you have
CONFIG_SECURITY_CAPABILITIES and CONFIG_SECURITY_FILE_CAPABILITIES
enabled. The Debian kernels are fine.
$ ls -l /bin/ping
-rwsr-xr-x 1 root root 30736 2007-01-31 00:10 /bin/ping
^
That is not good.
$ sudo chmod 755 /bin/ping
Or use dpkg-statoverride.
$ ls -l /bin/ping
-rwxr-xr-x 1 root root 30736 2007-01-31 00:10 /bin/ping
That is better but ping fails.
$ ping -c1 localhost
ping: icmp open socket: Operation not permitted
Now set the missing capability:
$ sudo setcap cap_net_raw+ep /bin/ping
... and ping will work again.
$ ping -c1 localhost
PING localhost (127.0.0.1) 56(84) bytes of data.
64 bytes from localhost (127.0.0.1): icmp_seq=1 ttl=64 time=0.026 ms
--- localhost ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.026/0.026/0.026/0.000 ms
Torsten Werner